1. Field of the Invention
The present general inventive concept relates to an inkjet image forming apparatus, and, more particularly, to an inkjet image forming apparatus to efficiently remove gas present upstream of a filter on an ink path, and a method of controlling ink flow.
2. Description of the Related Art
Image forming apparatuses serve to develop an image on a printing medium according to an input image signal, and include printers, copiers, facsimiles, and devices combining functions thereof.
The image forming apparatuses can be classified, according to a printing method thereof, into electro-photographic image forming apparatuses and inkjet image forming apparatuses. Inkjet image forming apparatuses are adapted to print an image by discharging fine droplets of ink on a printing medium at desired positions.
Such an inkjet image forming apparatus includes an ink tank in which ink is stored, a print head having nozzles to inject ink onto a printing medium, and an ink path to connect the ink tank and the print head to each other.
If ink to be fed to the print head contains impurities such as dust, the nozzles provided in the print head become clogged with the ink, causing damage to the print head or a deterioration in printing quality. To solve this problem, a filter is disposed on the ink path, to remove impurities contained in the ink.
Meanwhile, air bubbles are present in the ink path because gas is introduced into the ink path. For example, air bubbles in the ink path may be generated as outside air is introduced into the ink path upon detachment/attachment of the ink tank, or may be generated as gas dissolved in the ink is separated from the ink.
The air bubbles present in the ink path have negative effects upon operation of the inkjet image forming apparatus. In particular, when ink containing a lot of air bubbles passes through the filter, a significant pressure drop occurs, preventing the ink from being smoothly fed into the print head and resulting in printing failure. Moreover, an interior pressure of the ink path exhibits an uneven variation while the ink passes through the filter, and this makes controlling an ink discharge operation of the print head is difficult.
To solve the above-described problems, removing air bubbles present upstream of the filter at an appropriate time (for example, during a warm-up operation of the image forming apparatus or prior to beginning a printing operation according to a printing command) is necessary.
As a conventional solution in relation to the above-described problems, Japanese Patent Laid-open Publication No. 2006-0051832 relates to a method of removing air bubbles using a suction force of a pump after capping a nozzle section of a print head. When a negative pressure is applied to the nozzle section and an ink path via operation of the pump, air bubbles present upstream of a filter forcibly pass through the filter, thereby being discharged to the outside through nozzles of the print head.
However, with the above-described method, removal of air bubbles requires an excessively high pressure because air bubbles, present upstream of the filter, must pass through the filter in the course of removing air bubbles. This requires the use of a large-scale and large-capacity pump, and is disadvantageous in view of simplification in configuration of the image forming apparatus and costs of the image forming apparatus.
Another problem of the method disclosed in the above document is that ink is discharged simultaneously when the pump suctions air bubbles, causing an unnecessary waste of the ink.
In addition, as disclosed in the above document, methods using the pump cannot be easily applied to a print head (a so-called array print head) in which a nozzle section has a length corresponding to a width of a printing medium.